Control circuit for a blood fractionation apparatus

ABSTRACT

An apparatus for the continuous flow fractionation of whole blood incorporates motor driven whole blood, anticoagulant and replacement pumps, negative and positive pressure monitors, and a dual bubble detector which function in conjunction with a disposable single-use flow system and a hollow fiber filter to separate and collect plasma from whole blood. Operation of the pump motors, pressure monitors and bubble detector is controlled by a control circuit within the apparatus to provide one of several operator-selected operating modes, including run, prime and reinfuse modes. The control circuit provides an alarm which can be cancelled by the operator when certain system parameters fall outside of normal operating limits, and interrupts operation of the pumps when the parameters exceed maximum limits. A failsafe circuit independent of the control circuits interrupts power to the pump motors in the event the motors do not stop upon detection of a bubble or fluid absence in the flow system.

BACKGROUND OF THE INVENTION

The present invention relates generally to apparatus for processingwhole blood, and more specifically to blood fractionation apparatus forseparating and collecting a desired blood component, such as plasma.

Various methods and apparatus have been developed for the continuousflow processing of whole blood, wherein whole blood is taken from a livedonor, a desired blood component is separated and collected, areplacement fluid is added to the processed blood, and the processedblood is returned to the donor. Blood components typically collectedusing such processing include plasma (plasmapheresis), white blood cells(leukopheresis) and platelets (plateletpheresis).

Continuous flow blood processing apparatus may be of the centrifugaltype, wherein the differing density of the collected blood componentcauses the component to congregate for collection at a particular radialdistance in a centrifuge, or may be of the filter type, wherein theparticle size of the collected component allows only that component topass through a filter membrane into a collection chamber. Filter typeapparatus is generally preferable for continuous flow plasmapheresisapplications, since such apparatus does not require complex rotatingmachinery and is more compact and less costly to manufacture.

One form of filter which is particularly attractive for use inplasmapheresis apparatus utilizes a plurality of parallel microporoushollow fibers arranged side-by-side in the form of a bundle within ahollow cylinder. As whole blood is caused to flow through the fibers theplasma component passes through the walls of the fibers to thesurrounding container, which forms a collection chamber from which thecomponent is transported to a collection bag. A preferred constructionand method of manufacture of such a hollow fiber filter is shown in thecopending application of Robert Lee and William J. Schnell, entitled"Microporous Hollow Fiber Membrane Assembly and Its Method ofManufacture", Ser. No. 278,913, filed June 29, 1981.

To preclude operation in the event of a mechanical malfunction, theplasmapheresis apparatus typically includes a plurality of devices whichmonitor the fluid flow system. One such device may be a bubble detectorof either the light or ultrasonic type which monitors a particularsegment of the tubing for fluid absence, such as might result from abubble or air in the system. Another such monitor device monitors foreither excessive negative pressure at the inlet of the system or toexcessive positive pressure downline of the whole blood pump.

In the operation of plasmapheresis apparatus it is necessary that theapparatus operate in various modes, including a purge mode fordisplacing air from the system, a run mode for performing theplasmapheresis process, and a reinfuse mode for returning fluid to thepatient. The apparatus therefore requires a control system which allowsthe selection of these modes quickly and without undue attention on thepart of the operator. The control circuit should include necessaryinterlocks to prevent inadvertent mis-selection of an operating mode,and should condition all elements of the processing apparatus, includingthe bubble detector and pressure monitoring devices.

The plasmapheresis apparatus should also include a failsafe controlcircuit independent of the control circuit which monitors all functionsand removes power from the pump motors when a stop is called for by thecontrol circuit and not responded to by the pump motor.

The present invention provides control systems for blood fractionationapparatus such as that utilized for plasma separation and collectionwherein a user-cancellable audible alarm is provided for a firstcategory of system parameters, a non-cancellable visual alarm andinterruption of operation are provided for a second category ofparameters, and wherein the operating mode and the operation of thepumps are continuously and independently monitored and operation of thesystem is terminated after a predetermined delay in the event of anuncorrected malfunction.

In addition, the plasmapheresis apparatus described herein provides forconvenient connection of an auxiliary collection monitoring andreplacement fluid ratio control apparatus such as that described in thecopending applications of Arnold C. Bilstad and John T. Foley, entitled,"Blood Fractionation Apparatus Having Collected Volume Display System",Ser. No. 330,899; "Blood Fractionation Apparatus Having Collection RateDisplay System", Ser. No. 330,901: and "Blood Fractionation ApparatusHaving Replacement Fluid Ratio Control System", Ser. No. 330,900; allassigned to the present assignee and filed concurrently herewith. Asdescribed in these applications this apparatus provides an exchange modewherein an operator-selected ratio between the volume of plasmacollected and the volume of replacement fluid added is automaticallymaintained; and an autologous mode wherein the replacement pump isconnected to withdraw fluid from the collection container for secondaryprocessing and return to the donor, and the operating rate of the pumpis automatically varied to maintain a constant plasma level in thecollection container.

SUMMARY OF THE INVENTION

The invention is directed, in a blood fractionation apparatus operablein conjunction with a disposable fluid flow system for separating andcollecting a blood fraction from whole blood, and including at least onemotor-driven pump for conveying blood through the flow system, atachometer associated with the motor, and a fluid absence monitoringdevice, to a failsafe control circuit comprising a flip-flop responsiveto an applied tachometer pulse from the pump motor for producing analarm output signal, a series-parallel counter having a reset input, aclock input and a series/parallel enable input, the counter requiring apredetermined number of applied clock pulses following application of aserial enable signal for producing an output, and means for applying theflip-flop output signal to the parallel-serial enable input to enablethe counter to a serial mode upon occurrence of the tachometer pulse.The control circuit further includes means for applying the output ofthe fluid absence device to the reset input to enable operation of thecounter upon the occurrence of an alarm condition, means for applyingclock pulses to the counter whereby the counter counts to zero uponbeing conditioned to a serial mode at the serial-enable input and uponbeing enabled at the reset input, and means responsive to the output ofthe counter for terminating operation of the apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention which are believed to be novel areset forth with particularity in the appended claims. The invention,together with the further objects and advantages thereof, may best beunderstood by reference to the following description taken inconjunction with the accompanying drawings, in the several figures ofwhich like reference numerals identify like elements, and in which:

FIG. 1 is a perspective view of plasmapheresis apparatus incorporating acontrol system constructed in accordance with the invention.

FIG. 2 is a functional block diagram partially in schematic form showingthe principal components of the plasmapheresis apparatus of FIG. 1.

FIG. 3 is an enlarged front elevational view of the control panel of theplasmapheresis apparatus of FIG. 1.

FIG. 4 is a functional block diagram partially in schematic form of thewhole blood pump motor control circuit of the plasmapheresis apparatusof FIG. 1.

FIG. 5 is a simplified schematic diagram of a portion of the motorcontrol circuit of FIG. 4 showing an alternative input circuit for usetherein to adapt the circuit for use in conjunction with the replacementpump motor.

FIG. 6 is a functional block diagram partially in schematic form showingthe anticoagulant pump motor control circuit of the plasmapheresisapparatus of FIG. 1.

FIG. 7 is a functional block diagram partially in schematic form of thepositive pressure monitor circuit of the plasmapheresis apparatus ofFIG. 1.

FIG. 8 is a functional block diagram partially in schematic form showingthe negative pressure monitoring circuit of the plasmapheresis apparatusof FIG. 1.

FIG. 9 is a simplified schematic diagram of the dual bubble detectorcircuit of the plasmapheresis apparatus of FIG. 1.

FIG. 10 is a simplified schematic diagram partially in functional blockform of the control system of the plasmapheresis apparatus of FIG. 1.

FIG. 11 is a simplified schematic diagram partially in functional blockform showing the display system of the plasmapheresis apparatus of FIG.1.

FIG. 12 is a simplified schematic diagram partially in functional blockform of the failsafe control system of the plasmapheresis apparatus ofFIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, and particularly to FIG. 1, a plasmapheresisapparatus 20 incorporating the present invention is seen to include atable-mounted processor unit 21 mounted on a pedestal 23 of conventionaldesign having a generally horizontal top surface 24 on which theprocessor unit is supported. It will be appreciated that the processorunit may be removed as necessary from table 21 and installed on othersurfaces. The apparatus preferably includes a pair of vertical supportpoles 25 and 26 attached to the rear surface (not shown) of theprocessor unit. A horizontal bar 29 may be provided between the twosupport rods to allow a plurality of collection and dispensingcontainers of conventional construction to be hung by means ofappropriate hangers.

The processing apparatus 20 operates in conjunction with a fluid circuitgenerally identified by the reference numeral 30 in FIG. 1 and shownschematically in FIG. 2. The fluid circuit 30 includes a plurality offlexible plastic tube segments which form fluid conduits between variouscomponents of the fluid circuit. As shown in FIG. 2, whole blood derivedfrom a donor is conveyed through a first tubing segment 31 and aperistaltic-type whole blood (WB) pump 32 to a hollow fiber-type filter33 mounted on support rod 25. The operation of the WB pump is monitoredby a positive pressure (+P) monitor circuit 34 connected to tubingsegment 31 downline of the WB pump by a tubing segment 35. Negativepressure, such as might occur upon the collapse of a vein, is monitoredfor by means of a negative pressure (-P) monitor circuit 36 connected totubing segment 31 upline of the WB pump 32 by a tubing segment 37.

To prevent blood from clotting while in process in the apparatusanticoagulant solution from a supply container 38 is introduced at thepoint of blood withdrawal through a tubing segment 39. Aperistaltic-type pump 40 is provided along tubing segment 39 to providea controlled rate of addition of the anticoagulant fluid to the wholeblood.

Plasma separated from the whole blood within the hollow fiber filter 33is conveyed by a tubing segment 41 to a plasma collection container 42.The pressure provided by WB pump 32 is sufficient to cause flow from thefilter to the collection container. The plasma-deficient processed bloodfrom filter 33 is conveyed through a tubing segment 43 to an ultrasonicbubble detector 44, which may be similar in structure and operation tothat described in the copending application of Arnold C. Bilstad andMichael Wicnienski, entitled, "Liquid Absence Detector", Ser. No.127,552, filed Mar. 6, 1980. Basically, this bubble detector 44 includesa hollow housing having an internal filter screen assembly 45. Anybubbles in the processed blood fluid collect at the upper portion of thehousing. An ultrasonic sound transmitter 46 and an ultrasonic soundreceiver 47 positioned at opposite sides of the upper portion of thehousing detect bubble formation. The source 46 and detector 47 areconnected to a dual bubble detector circuit 48 which provides first andsecond independent outputs upon the occurrence of a bubble or liquidabsence.

Replacement fluid is added to the plasma-deficient blood at thislocation through a tubing segment 50 which is connected at one end to areplacement fluid container 51 and at its other end to the housing ofbubble detector 44. A peristaltic-type replacement pump 52 is positionedalong tubing segment 50 to establish a controlled flow rate for thereplacement fluid. The combined plasma-deficient whole blood andreplacement fluid are pumped from bubble detector 44 back to the donorthrough a tubing segment 53.

As shown in FIG. 1, the plasmapheresis apparatus 20 is housed in acabinet 54 which includes a sloped upper portion on which a controlpanel 55 and the anticoagulant pump 40 are located. The cabinet alsoincludes a sloped lower portion on which the WB pump 32 and replacementpump 52 are mounted, together with the inlet to the positive pressuremonitor 34 and the inlet to the negative pressure monitor 36. When flowsystem 30 is installed on the plasmapheresis apparatus, theanticoagulant supply container 38, replacement fluid source container 51and plasma collection container 42 are suspended from the horizontalsupport bar 29 as shown, and the hollow fiber filter 33 is mounted bymeans of an appropriate mounting bracket 56 to vertical support rod 25.The bubble detector 44 is similarly mounted to support rod 25 by meansof a mounting bracket 57, and the ultrasonic source 46 and detector 47thereof are electrically connected to the processor housing by anelectrical cable 58.

Control panel 55 includes operator-actuated controls for operating theplasmapheresis apparatus. These include a selector switch 60 by whichthe operating speed of the anticoagulant pump 40 is set, a potentiometercontrol 61 and digital readout 62 by which the operating speed of the WBpump 32 is controlled, and a potentiometer 63 and digital readout 64, bywhich the operating speed of the replacement pump 52 is controlled. Aplurality of pushbutton switches 65 are provided to establish theoperating mode of the apparatus, and a plurality of status-indicatinglights 66 provide indications of malfunctions in the system. A connector67 (FIG. 2) on the back panel of the processor enables an auxiliarycollection monitoring and replacement fluid ratio control apparatus aspreviously described to be readily connected.

Referring to FIG. 2, the whole blood pump 32 is driven by a motor 70having a mechanically coupled tachometer 71. Power for operating motor70 is provided by a motor control circuit 72 which responds to ratesetting means in the form of potentiometer control 63 and a tachometerfeedback signal from the tachometer 71 to maintain a desired motoroperating speed. The actual pump flow rate is displayed by readout 62 aspart of a display circuit 75 which receives the tach output signal fromtachometer 71.

Similarly, the replacement pump assembly 52 is driven by a motor 76having an associated tachometer 77. Power for motor 76 is provided by amotor control circuit 78 which responds to a tach feedback signal fromtachometer 77 and the rate selected by the panel-mounted potentiometer63 to maintain a desired constant motor speed. The actual pump flow rateis displayed by readout 64 as part of the display circuit 75.

The anticoagulant pump 40 is driven by a stepper motor 78. Drive signalsfor motor 79 are developed by a motor control circuit 80 which respondsto rate selection switch 60 to maintain a desired anticoagulant flowrate. A tachometer associated with motor 79 provides tach pulses for useby other circuits of the apparatus.

The operation of the various pump motors is controlled by a processorcontrol circuit 81 which includes five mode select pushbuttons 66 onfront panel 55. System malfunctions, such as negative pressure atpressure monitor 36, or excessive positive pressure at pressure monitor34, or the occurrence of a bubble or other fluid absence as signaled atthe first output (BD1) of bubble detector circuit 48, result in theapplication of a signal to processor control circuit 81. This circuitresponds by producing a control signal on a first motor control line 82to the motor control circuits 72, 78 and 80 to interrupt operation ofthe motors. In addition, an alarm 83 associated with the processorcontrol circuit may be sounded and an appropriate one of indicator lamps66 may be lit to alert the operator.

The plasmapheresis apparatus 20 further includes a failsafe controlcircuit 84 which functions to remove power from the pump motors in theevent that processor control circuit 81 fails to respond to a systemmalfunction. To this end, the outputs of the motor tachometers areapplied to the failsafe circuit, together with the second output (BD2)of bubble detector 48. Upon the occurrence of a bubble or fluid absence,as signaled by bubble detector circuit 48, failsafe circuit 84determines from the simultaneously applied tach output signals whetherthe pump motors have in fact stopped and, if motion is detected after aperiod of time, provides an additional stop signal which removes motoroperating power to motor control circuits 72 and 78 on a second motorcontrol line 85.

Referring to FIG. 3, operator designation of the operating mode ofplasmapheresis apparatus 20 is accomplished by five push button switches90-94 which are mounted on control panel 55 and which designate prime,run, reinfuse, mute and reset operating instructions, respectively.Operation in the prime, run and reinfuse modes is indicated by indicatorlamps 95-97, respectively. An emergency stop switch 98 associated withfailsafe circuit 84 provides an additional means of stopping theapparatus in an emergency. The occurrence of a abnormal condition suchas an emergency stop, a pump door being opened, a bubble being detected,limits being exceeded by either the positive pressure or negativepressure monitors, or a ratio being exceeded by an auxiliary collectionmonitor and ratio control apparatus (if installed), is indicated byindicator lamps 100-105 on control panel 55.

Referring to FIG. 4, operating power is supplied to the WB pump motor 70through a motor control circuit 72 comprising the normally open contactsof a motor control relay 110, a series-connected power transistor 111,and a reactance control network 113B comprising a series-connectedinductance and a shunt-connected capacitor 113A. The series combinationof these components supplies power from a unidirectional motor currentsource (not shown in FIG. 4) to the motor. The return line from themotor includes a series-connected current metering resistor 114.

Pump motor 70 is a direct current type motor and receives excitationover a variable duty cycle through power transistor 111. The conductionof this transistor is controlled by excitation control means in the formof a pulse width modulator 115 which provides an appropriate controlsignal to the base electrode of the transistor.

Tachometer 71, which is seen to include a light source 116, a slotteddisc 117 and a photodetector 118, operates in a conventional manner toprovide output pulses indicative of incremental rotation of the pumpmotor. These pulses are applied to a first amplifier 120 wherein theyare amplified for use by other systems within the plasmapheresisapparatus, and to a second amplifier 121 wherein they are amplified forapplication to a frequency to analog converter circuit 122. This circuitdevelops an analog output signal amplitude-dependent on the frequency ofthe tach pulses. This signal is applied to the inverting input of acomparator amplifier 123, wherein it is compared with a speed controlsignal applied to the non-inverting input from potentiometer 61 throughan analog switch device 124. The control gate of switch device 124 isconnected to the first pump control line 82 so that in the absence of anappropriate output signal from control circuit 81 enabling the motor noreference signal is applied to the non-inverting input of comparator123.

Comparator amplifier 123 operates in a conventional manner to produce anoutput signal indicative of the difference between its inputs. Thisdifferential signal is applied through an isolation circuit 125 to pulsewidth modulator 115, wherein it controls the duty cycle of powertransistor 111, and hence the speed of pump motor 70.

By reason of the action of comparator 123 in comparing thespeed-dependent tach signal with the operator-set reference signal frompotentiometer 61,a closed loop system is formed whereby motor 70 ismaintained at an operator-designated speed. Any change in pump speedtending away from the designated speed is automatically compensated forby a corresponding correction in the duty cycle of transistor 111.

To provide protection against overspeed operation, the excitation levelapplied to pump motor 70 is continuously monitored by an overspeeddetection circuit 126. In the event of an overspeed condition, thiscircuit produces an output which is coupled through an OR gate 127 to analarm output bus 128, and through OR gate 127 and a second OR gate 130to the inhibit input of pulse width modulator 115, wherein it preventsthe application of current to the base of transistor 111, therebystopping the motor.

The remaining input of OR gate 130 is connected to a failsafe inhibitline 131 connected to the failsafe control line 85 of the plasmapheresisapparatus. Application of an inhibit signal to this control line byfailsafe circuit 84 results in pulse width modulator 115 beinginhibited. Additional protection against uncontrolled operation of pumpmotor 70 is provided by relay 110. This relay must be energized througha pair of relay control lines 132, 133 in order for the pump motor 70 toreceive operating power. As will be seen presently, the presence of anenabling control signal on these lines is dependent on the failsafecontrol system 84 of the apparatus.

As an additional safety measure, WB pump 32 has associated with it adoor switch 137 which provides an open circuit in the event the pumpdoor is opened. This contact action is used to inhibit pulse widthmodulator 115 to prevent further operation of the pump, and provide anoutput on a door open line 134 to control circuit 81.

An alternative input circuit which allows the WB pump motor controlcircuit 72 to function as the replacement pump motor control circuit 78is shown in FIG. 5. As seen in FIG. 2, the replacement pump motorcircuit 78, in the manner of motor control circuit 72, produces astall/overspeed alarm on a control line 135 and provides a motor tachoutput signal on a control line 136. Also, pump control circuit 78receives inputs from the pump enable line 82, the failsafe inhibit line85, and the failsafe motor enable relay lines 132, 133.

The replacement pump rate control potentiometer 63 includes a switch 140which is closed upon the potentiometer being turned to its minimum ratefully counterclockwise position. This causes an enabling signal to beapplied through an inverter amplifier 141 to a first AND gate 142,thereby allowing a pump enable control signal on line 82 to be appliedthrough gate 142 to the gate electrode of a first analog switch device143. This enables switch 143 and allows an analog pump speed controlsignal developed by the previously described optional collection rateand replacement fluid ratio control apparatus to control the speed ofreplacement pump motor 76. At the same time, the closure of contact 140results in a second AND gate 144 being inhibited through a non-invertingamplifier 145, thereby preventing the enabling signal on line 82 fromconditioning a second analog switch device 146 in series with the arm ofpotentiometer 63 to a conductive mode.

When the optional replacement fluid rate control apparatus is notconnected or is not in use, potentiometer 63 is positioned mid-range andswitch 140 is open. This results in analog switch device 146 beingenabled so that motor speed is determined by the position of the arm onpotentiometer 63. At the same time, analog switch device 143 isinhibited, and analog control signals from the option, if present, haveno effect on the speed of the motor.

Referring to FIG. 6, multi-phase drive signals are applied to theanticoagulant pump stepper motor 78 by a conventional stepper motordrive circuit 150. The signals are applied through respective ones ofisolation devices 151-154 and transistors 155-158. Isolation devices151-154, which may be conventional electro-optical devices, areconnected by respective resistors 160-163 to a source of unidirectionaloperating current, and terminals by respective ones of resistors 164-167to the motor power supply (not shown in FIG. 6). An additional resistor168 supplies power to the stepper motor. Control pulses for initiatingsequencing pulses from stepper motor drive circuit 150, and consequentlyeach incremental rotation of the motor, are provided by a clock 170.Output pulses from the clock are applied through a distribution line 171and an analog switch device 172 to a rate multiplier 173. Ratemultiplier 173, which may be conventional in structure and operation,responds to an operator-selected rate set by switch 60 to provide apreselected rate multiplication to the applied clock pulses. Thisresults in stepper motor drive circuits 150 being impulsed at auser-selected rate, and consequently the stepper motor 79 being drivenat the desired rate.

Control over operation of stepper motor 79 is obtained by applying thepump enable control signal developed on line 82 by control circuit 81 toanalog switch device 172 through an AND gate 174. The remaining input ofAND gate 174 is connected to a separate pump enable control line 175whereby control circuit 81 initiates anticoagulant pump operation onlyduring the run and prime modes.

As an additional precaution against uncontrolled operation, current fromthe motor power source (not shown in FIG. 6) is applied to stepper motor79 through the normally open contacts of a motor control relay 176. Thisrelay, like similar relays in the WB and replacement motor controlcircuits 72 and 78, is energized by an enable signal on lines 132, 133during normal operation of the system failsafe control circuit 84.

The anticoagulant pump tachometer 176 includes a light source 177, aslotted disc 178 and a photodetector 179. As disc 178 turns with motor79, output pulses produced at photodetector 179 are supplied through afirst inverter amplifier 180 to an anticoagulant tach output line 181for application to failsafe circuit 84. Pulses are also supplied througha second inverter amplifier 182 to the input of a flip-flop 183 whereinthey are conditioned for application to the parallel enable (PE) inputof a programmable down counter. Upon application of each such tachoutput pulse, down counter 184 assumes a predetermined initial count, asdetermined by a hard-wired binary input. In the illustratedplasmapheresis apparatus a 64 is thus loaded.

Counter 184 is counted down from the parallel-loaded 64 initial countingstate by output pulses from rate multiplier 173 until a zero count isreached, at which time the counter produces an output which is appliedthrough an inverter amplifier 185 to the stall alarm line 186 associatedwith the anticoagulant pump. As will be seen presently, this has theeffect of signaling a stall condition to failsafe control circuit 83 andthereby stopping operation of the plasmapheresis apparatus. No stallalarm signal is produced as long as stepper motor 79 accomplishessufficient movement to produce an output from photodetector 179 before64 control pulses from rate multiplier 173 are applied to down counter184, since 64 pulses are required before the down counter reaches a zerocounting state. In this way, stall protection is provided foranticoagulant pump 40. A door switch 187 associated with the pumpprovides a door open signal on line 135 when the pump door is open.

Referring to FIG. 7, the positive pressure monitor circuit 34 includes apressure transducer 190 of conventional construction. This transducerincludes a tubing connection port (FIG. 1) which extends through thelower sloped panel of the apparatus housing to receive tubing segment 35from flow set 30. Transducer 190, in accordance with conventionalpractice, forms a resistive bridge network 191 wherein the outputresistance varies as a function of applied pressure. The outputterminals of this bridge network are connected through respectiveresistors 192 and 193 to the inverting and non-inverting inputs of adifferential amplifier 194. The output of this amplifier, which dependson the applied differential voltage, and hence on the pressure appliedto transducer 190, is connected to a voltage-to-frequency converter 195.The output is also connected to the inverting input of the amplifierthrough a resistor to provide degenerative feedback.

Voltage-to-frequency converter 195 responds to the applied voltage toproduce an output having a frequency related to the pressure present attransducer 190. This pressure-related signal is applied through an ANDgate 196 to the clock input of a serial-parallel counter 197, and to aline 199 to provide a variable frequency pressure-indicative signal foruse by display circuit 75. Upon the application of a clock pulse to theasynchronous parallel enable (APE) input of counter 197, the counter inaccordance with conventional practice assumes an initial counting stateequal to an applied hard-wired binary signal. Upon completion of theclock pulse the counter is counted down by each output pulse fromconverter 195 until reaching a zero count, at which time it produces anoutput signal. This signal is applied through an inverter amplifier 198to a positive pressure alarm line 200 for application to control circuit81. In addition, the output is applied to the remaining input of ANDgate 196 to inhibit the application of further converter output pulsesto the counter after completion of the count.

The effect of counter 197 is to establish a limit to the outputfrequency of converter 195 above which a positive pressure alarm issignaled. In practice, a count of 180 is hard-wired for loading intocounter 197 once each second upon receipt of a one second clock pulse.If one count at the output of converter 195 is made to equal 1millimeter of Hg, as in the illustrated plasmapheresis apparatus, then180 mm Hg is established as the limit. If the frequency of the output ofconverter 195 is below 180, corresponding to a pressure less than 180 mmHg, then counter 197 does not reach a zero state and no positivepressure alarm is produced on line 200. Conversely, if the count exceeds180, corresponding to a pressure in excess of 180 mm Hgl, counter 197reaches a zero count and an alarm is produced.

To provide a necessary offset for converter 195 the noninverting inputof differential amplifier 194 and the reference input terminal ofconverter 195 are connected in a conventional manner to an offsetvoltage source comprising a resistor 201 and a diode 202 connectedbetween ground and a source of current. Gain adjustment and temperaturecompensation are also provided in the supply circuit for transducer 190,which comprises a gain adjust potentiometer 203, a resistor 204, adifferential amplifier 205 and a diode 206.

Referring to FIG. 8, the negative pressure monitor circuit 36 includes apressure transducer 210. This pressure transducer provides a resistivebridge network 211 having its output terminals connected to thenon-inverting inputs of respective differential amplifiers 212 and 213.The output of amplifier 212 is connected to the inverting input of theamplifier, and through a resistor 214 to the non-inverting input of athird differential amplifier 215. The output of differential amplifier213 is connected to the inverting input of the amplifier, and through aresistor 216 to the inverting input of differential amplifier 215. Theoutput of differential amplifier 215 is connected directly to theinverting inputs of a pair of comparators 216 and 217, and through aresistor 218 back to the inverting input of the amplifier.

A reference voltage is applied to comparator 217 by a potentiometer 220connected between a voltage regulator 221 and ground. Similarly, areference voltage source is applied to differential amplifier 216 bymeans of a potentiometer 222 connected between the reference voltagesource and ground. One input terminal of the resistive bridge network211 is connected to the output of voltage regulator 221, and the otherinput terminal is connected to ground.

In operation, an output voltage is produced by pressure transducer 210in a conventional manner. This voltage is applied through differentialamplifiers 212 and 213 to the inverting and non-inverting inputs ofdifferential amplifier 215 to produce an output voltage from that deviceindicative of applied pressure. This output voltage is compared bycomparator 217 against a reference voltage established on the arm ofresistor 220. When this reference voltage is exceeded, differentialamplifier 217 produces an output which is recognized on a line 223 as anegative pressure warning by control circuit 81. Similarly, indifferential amplifier 216 the applied output signal is compared againsta reference established by potentiometer 222 and an alarm is produced ona line 224 when the reference is exceeded.

In practice, the reference set by potentiometer 222 is higher than thatset by potentiometer 220, so that a warning output is produced prior toan alarm output. This is advantageous, since it allows the attendant,once aware of the impending low pressure alarm condition, to takeremedial action, as by adjusting the interface between the donor and thesystem prior to an alarm level condition developing. As will be seenpresently, the control system of the present invention facilitates suchremedial action.

Referring to FIG. 9, the bubble detector circuit 48 includes first andsecond signal channels, providing first and second independent alarmoutputs. A single ultrasonic oscillator 230 drives transducer 46.Ultrasonic energy passing through the fluid medium within the bubbledetector chamber is received by transducer 47, which produces an ACoutput signal dependent on the intervening medium.

In the first signal channel, the output of transducer 47 is coupledthrough a capacitor 231 to the input of an amplifier 232. The output ofthis amplifier is connected through a resistor 233 to ground and througha capacitor 234 to a pair of diodes 235 and 236. Diode 235 is connectedto ground to peak limit the output signal at a predetermined thresholdlevel, and diode 236 is connected to the inverting input of adifferential amplifier 237 and by a resistor 238 and a capacitor 239 toground to provide peak detection for the output signal developed byamplifier 232.

A reference voltage is applied to the non-inverting input of comparatoramplifier 237 by a voltage divider comprising resistors 240 and 241connected between a system current source and ground. The junction ofthese resistors is coupled by a resistor 242 to the non-inverting inputof the comparator. The output of the comparator is connected through aresistor 243 to a line 244 by which the occurrence of a bubble or fluidabsence is signaled to the system control circuit 81. At the same time,the output of amplifier 237 is coupled back to the non-inverting inputof the amplifier by a resistor 245 to provide regenerative feedback.

In operation, when the detected signal applied to comparator 237 fallsbelow the reference level applied to the non-inverting input,thecomparator provides an output (BD1) on line 244 which is recognized asthe occurrence of a bubble or fluid absence. Amplifiers 232 and 237, aswell as the voltage divider comprising resistors 240 and 241, aresupplied by a positive polarity unidirectional current source derivedfrom the main power supply of the apparatus. In contrast, as will beseen presently, the same components in the second bubble detectorchannel are supplied by current derived from a separate supplyassociated with failsafe control circuit 84.

The second bubble detector channel is identical in structure andoperation to that of the first channel with the exception of utilizingthe failsafe circuit power supply as its power source. The secondchannel includes a capacitor 246 which couples the output of transducer47 to an amplifier 247. The output of this amplifier is connected toground by a resistor 248 and through a capacitor 250 to diodes 251 and252. Diode 251 is connected to ground to provide peak limiting action,and diode 252 is connected to the inverting input of a comparatoramplifier 253 and to ground by the parallel combination of a resistor254 and a capacitor 255. This provides peak detection for the receivedsignal.

A reference voltage is developed at the non-inverting input ofcomparator 253 by a voltage divider comprising a pair of resistors 256and 257. The juncture of these resistors is connected to thenon-inverting input of the amplifier by a resistor 258. The output ofcomparator amplifier 253 is connected through a resistor 260 to a secondalarm line 261 to provide a second bubble detector (BD2) alarm outputfor utilization by failsafe control circuit 84. The output of comparator253 is also coupled by a resistor 262 to the non-inverting input of thedevice to provide regenerative feedback. The operation of the secondbubble detector channel is identical to that of the first bubbledetector channel.

Referring to FIG. 10, plasmapheresis apparatus 20 includes, inaccordance with one aspect of the invention, a control circuit 81 whichcoordinates the operation of the pump motors 70, 76 and 79 andmonitoring devices 34, 36 and 48 in discrete reset, prime, run andreinfuse operating modes, while providing in the event of abnormalsystem parameters an audible warning which can be reset by the operatorwhile retaining a visual indication of the abnormal parameter. Toinitiate a plasmapheresis procedure the operator momentarily depressesthe prime switch 90. This provides a signal through a non-invertingamplifier 262 to an RS-type mode control latch 263, which is conditionedby the signal to a reset mode. The output of latch 263 is applied toPRIME LED 95 to indicate that a prime mode has been selected. The outputof the latch is also applied to one input of an OR gate 264. The outputfrom this gate conditions an RS latch 265 to a set mode, which providesan output signal on thepump enable control line 82 to enable the threepumps of the apparatus in the manner previously described. The output oflatch 263 is also applied to an OR gate 266, which provides a totalvolume reset signal on reset line 113 for utilization by the optionalcollection monitor and ratio control unit.

Upon completion of the prime procedure, run switch 91 is momentarilydepressed. This causes a mode control latch 268 to be conditioned to itsset mode through a non-inverting amplifier 270. The resulting outputfrom latch 268 is applied to an OR gate 271 to provide a reset pulse forresetting latch 263, and to run LED 96 to provide a front panelindication that the apparatus is in the run mode. The output of latch268 is also applied to an OR gate 272 and to a remaining input of ORgate 264. The resulting output of OR gate 272 provides an enablingsignal for bubble detector No. 2 on a control line 273 for use byfailsafe circuit 84, and an enabling input to an AND gate 274 associatedwith the set input of an RS-type alarm latch 275. The output from ORgate 264 operates in the manner previously described to condition latch265 to a set state to provide a pump enabling signal on the first pumpcontrol line 82.

The remaining input of AND gate 274 is connected to the output of theNo. 1 bubble detector (BD1) by line 244, so that upon the occurrence ofa fluid absence in the run mode the BD1 output signal conditions RSlatch 275 to a set mode. The BD1 output line 245 is also connected to anOR gate 276. The output of this gate is connected to one input of an ANDgate 277. The output of AND gate 277 is connected to bubble trap, LED103, which provides a front panel indication of a fluid absence in thesystem. By reason of OR gate 276 and AND gate 277 LED 103 is caused tolight when a fluid absence is detected, even if alarm latch 275 is notconditioned to its set mode by reason of the apparatus not being in therun mode and AND gate 274 being inhibited.

To begin the reinfuse mode the operator momentarily depresses switch 92to condition an RS-type latch 278 to its set mode through anon-inverting amplifier 280. The resulting output from latch 278 isapplied to an input of OR gate 264, to an input of OR gate 271, to aninput of OR gate 272 and to reinfuse LED 97. LED 97 lights to indicateon control panel 55 that the reinfuse mode is in use. A signal is alsoprovided on control line 175 to inhibit operation of the anticoagulantpump 40, as previously described. The output of latch 278 is alsoapplied to one input of an OR gate 281 to reset latch 268, and to oneinput of OR gate 271 to reset latch 263. The output of OR gate 264conditions latch 265 to its set mode, thus enabling the apparatus pumpsthrough pump control line 82, in the manner previously described. Theoutput of OR gate 272 enables the output of BD2 in failsafe controlcircuit 84, and enables AND gate 274 to the set input of latch 275, inthe manner previously described.

To terminate operation the operator momentarily depresses switch 94,which applies a reset signal through an OR gate 282 to the reset inputsof the three mode control latches 263, 268 and 278 to reset theselatches to their reset states. Consequently, the pump motors stop as thepump enable control signal is removed from motor control line 82. Areset signal generated on a reset line 283 during initial power-up ofthe apparatus by a power-up circuit 284 is applied to the other input ofOR gate 282, and to the remaining input of OR gate 266 to cause a totalvolume reset signal on a reset line 113 at connector 67.

The output of OR gate 282 is applied to one input of an OR gate 285. Theoutput of this gate is applied through an inverter amplifier 286 to thereset input of latch 265, through an inverter amplifier 289 to the resetinput of latch 278, and to the remaining inputs of OR gates 271 and 281.Consequently, upon initial power-up of the apparatus latches 263, 268and 278 are reset and RS latch 265 is conditioned to a reset mode, sothat no pump enable signal is present on pump control line 82.

The pumps are also disabled upon one or more of the pump doors beingopened, which it will be recalled result in a signal on the door opensignal line 135. Within control circuit 81 the door open line 134 isconnected through a non-inverting amplifier 287 to another input of ORgate 285 to condition RS latch 265 to a reset state. Also, the output ofamplifier 287 is applied through an inverter 288 to LED 100 to indicateon control panel 55 that a door is open.

In the event of a positive pressure alarm on line 200, which it will berecalled occurs should the pressure downline of the WB pump exceeds apredetermined level, an RS-type latch 290 is conditioned to a set state.The resulting output from latch 290 is applied to one input of a foursection shift register 291, to one input of a NAND gate 292, to oneinput of an AND gate 293, and to one input of an OR gate 294. The outputof AND gate 293 is connected to cell pressure LED (+P) 102, causing thatdevice to light to signal a positive pressure alarm.

In the event of a negative pressure alarm on line 244, which occurs as aresult of excessive negative pressure upline of the WB pump, an RS-typelatch 295 is conditioned to a set mode. The resulting output from latch295 is coupled to a second input of shift register 291, to one input ofa NAND gate 296, to one input of an OR gate 297, and to one input of ORgate 294. The resulting output from OR gate 297 is applied through anAND gate 298 to inlet line (-P) LED 104, resulting in a negativepressure alarm on the apparatus control panel. The application of thesignal to OR gate 294 results in latch 265 being conditioned to a resetstate to terminate operation of the pump motors.

Receipt of a negative pressure warning on line 223 results in a signalbeing applied to the remaining input of OR gate 297. As a consequence,the output from OR gate 297 is applied through AND gate 298 to the inletline (-P) LED 101 to provide a warning of an impending negative pressurealarm condition. Since the alarm condition occurs at a lower pressurelevel than the alarm condition, upon receipt of the warning the operatorwill have time to take corrective action before the occurrence of analarm condition.

Upon occurrence of BD1 output latch 275 is conditioned to its set mode.The output of latch 275 is applied to a third input of shift register291, to the remaining input of OR gate 276, to an input of NAND gate301, and to an input of OR gate 294. OR gate 294 functions in responseto the applied signal to condition RS latch 265 to a reset state todisable the pump motors. OR gate 276 provides an output through AND gate277 which causes the bubble trap LED 103 to light.

One feature of the optional collection monitor and ratio controlapparatus described in the previously identified copending applicationsof Arnold C. Bilstad and John T. Foley is that an over limit signal isgenerated upon the counters incorporated therein reaching excessivelyhigh counting states, as might result from a malfunction of theapparatus of the monitoring device. The resulting over limit signal isavailable on a line 112 at connector 67 for application to controlcircuit 81, wherein it is applied to a fourth input of shift register291, to a NAND gate 302, to an input of AND gate 303 and to an input ofOR gate 294. As a consequence, the output of AND gate 303 causes LED 105to light to indicate an overlimit condition, and the motor control latch265 is conditioned to a reset state to disable the pump motors.

The outputs of alarm latches 290, 295 and 275, which comprise firstlatch means, and the overlimit control line 112, are connected torespective inputs of second latch means, in the form of the four inputshift register 291. The same alarm signals are also each connected toone input of respective ones of the four NAND gates 292, 296, 301 and302, which comprise part of an alarm circuit means. Shift register 291,which may be conventional in structure and operation, has four outputs.These outputs are each connected to a remaining input of respective onesof the NAND gates. The remaining inputs of NAND gates 301-304 areconnected by a line 305 to a source of pulse signals, in this case a 1hertz clock signal source 304. The outputs of NAND gates 292, 296, 301and 302 are connected to remaining inputs of respective ones of ANDgates 293, 298, 277 and 303, and to respective inputs of a four inputNAND gate 306. The output of NAND gate 306 is connected to alarm 83.

The effect of the 1 hertz pulses on line 305 is to alternately enableand inhibit NAND gates 292, 296, 301 and 302 on a one second cyclicalbasis. As will be seen, this causes alarm 83 and the corresponding LEDfor an occurring fault to flash at a one second rate.

In a no-fault condition, the outputs of latches 290, 295 and 275, andthe signal on overlimit line 112, are all logic low. This causes theNAND gates to be inhibited, with the result that each provides a logichigh output. These outputs enable AND gates 293, 298, 277 and 303,allowing LED 101 to light upon receipt of a negative pressure warning online 223, and LED 103 to light upon the absence of fluid at bubbledetector 44. Since NAND gate 306 is enabled and provides a logic lowoutput, alarm 82 is not activated. Since all inputs to OR gate 294 arelow, no output is provided and latch 265 is conditioned according to theoperating mode selected by mode control latches 262, 270 and 280.

In the event of an operating fault, such as a positive pressure alarm,latch 290 (or the latch appropriate to the particulat alarm) isconditioned to its set state. This produces a logic high which isapplied to shift register 291, NAND gate 301, AND gate 293 and OR gate294. OR gate 294 responds by conditioning latch 265 to its reset stateto stop the pump motors. Shift register 291 does not immediately respondto the change in input, since a clock pulse is required before theregister output will latch to the applied input state. Consequently, theoutput of the shift register remains high.

As a consequence of the change of state at the input of NAND gate 292(two of the three inputs being logic high) gate 292 provides alternatelyhigh and low output states according to the state of line 305. Thiscauses AND gate 293 to be alternately inhibited and enabled, so thatwith the steady logic high from latch 290 applied to its other input, itprovides a flashing output for LED 103. At the same time, the periodicchange of state of one of the inputs of NAND gate 306 results in analternately logic high and logic low output being applied to alarm 83,so that the alarm pulsates at the clock rate.

The alarm and the LED associated with the alarm condition continue topulsate until the operator momentarily depresses the mute alarm switch93. This causes a momentary clock pulse to be applied to shift register291. Upon receipt of the clock pulse, the shift register, in accordancewith conventional operating principles, changes its output state to thecomplement of the input state. Consequently, the output of the registercorresponding to the positive pressure monitor assumes a logic low,while the remaining outputs of the register remain logic high. The logiclow, applied to NAND gate 292, causes that gate to be continuouslyinhibited. Since the output of NAND gate 292 is logic high, the outputof NAND gate 306 is a steady logic low which does not activate alarm 83.Also, AND gate 293 is now continuously enabled so that LED 103 issteadily illuminated.

Thus, an initial alarm condition results in a pulsating aural alarm anda flashing visual alarm. The operator, having noted an aural alarmcondition, can silence the alarm and change the lamp to steady by merelypressing the mute switch. This is a great advantage in often busyclinical and hospital environments, where it may not be possible toimmediately remedy an alarm situation, but yet it is necessary toautomatically provide a reminder of the alarm having been sounded.

The operation of the alarm feature of the control circuit is identicalfor the negative pressure alarm, the bubble detector alarm, and theoverlimit alarm. In each case a corresponding lamp flashes and the alarmsounds intermittently until the mute alarm switch 93 is depressed, afterwhich the alarm is muted and the lamp lights continuously.

It will be noted that BD1 is enabled as an alarm condition only when theapparatus is in its run or reinfuse modes. This is to prevent the bubbledetector from providing an alarm which terminates operation during theprime mode, when air in the lines is normal. However, OR gate 276 allowsthe bubble trap, LED 102 to light during the prime mode to indicate thatthe bubble detector is operative.

Referring to FIG. 11, within display circuit 75 the pulses from thereplacement motor pump tach 77 on line 136 are applied through aninverter 310 and counter 311 to an AND gate 312. Counter 311 is set todivide by a factor of 160, producing one output pulse for each 160 inputpulses from inverter 310. If AND gate 312 is enabled, thefrequency-divided pulses are applied through an OR gate 313 to the clockinput of a display counter 314. Counter 314, which may be conventionalin structure and operation, responds to the applied pulses to accumulatea count indicative of the volume in milliliters pumped by replacementpump 52. At the end of the measurement period, in this case one second,a latch pulse is applied to counter 314 to cause the counter in aconventional manner to assume the accumulated count and provide anappropriate driving signal for a trio of associated seven segmentdisplay panels 315-317, which comprise readout 64 on panel 55.Appropriate strobe pulses for enabling the displays are provided bycounter 314 through respective ones of inverter amplifiers 318-320.

Following the latch pulse, after the display counter has assumed at itsoutput the previously accumulated count, the accumulated count is resetby a reset clock pulse (T₂) applied to the reset input of the counter.This reset pulse, and a corresponding latch pulse (T₁), are developed ata one second repetition rate by a Johnson counter 321. This counter isclocked by a one hertz signal obtained from a clock circuit, whichincludes an oscillator 323 and frequency divider 324 of conventionaldesign. Since alternate outputs of the Johnson counter are utilized, thelatch pulse leads and is distinct from the reset pulse, so that counter314 completes its latch function before it begins its reset function,thus assuring that the counter will display the preceeding count duringthe subsequent one second counting interval.

The replacement rate display 64 can be alternatively switched to adisplay of fluid pressure at the output of the WB pump by momentaryactuation of a push button switch 325. This causes AND gate 312 to beinhibited through a non-inverting amplifier 326, and an AND gate 327 tobe enabled through an inverter 328. As a result, the variable frequencypositive pressure pulses at 10 hertz per millimeter of mercury developedon line 199 by the positive pressure monitor 34 are supplied to displaycounter 314 through a non-inverting amplifier 330, a divide-by-tencounter 331, and OR gate 313. Since counter 314 continues to be resetonce each second, the counter in effect measures the frequency in hertzper second, which translates directly to millimeters of mercury. Anindication is given of the display selected for readout 64 by LEDindicators 331 and 332. When display select switch 325 is not actuated,as during normal operating conditions, LED 332, indicating a reinfuserate reading, is powered through inverting amplifier 333. When displayselect switch 325 is actuated, LED 331, indicating a pressure reading,is illuminated through non-inverting amplifier 334

The whole blood flow rate, and the total volume of whole bloodprocessed, may be similarly read on readout 62. To this end, the outputof the WB pump tach 71, on line 119, is applied through an inverter 335to the input of a divide-by-160 counter 336. The output of this counter,which comprises 60 pulses per milliliter pumped by the WB pump, isapplied to the clock input of a latch-type display counter 337. Thiscounter, which may be conventional in structure and operation, countsthe applied pulses until a T₁ (latch) clock pulse is applied to itslatch input through an inverter 338, at which time the accumulated countis latched and a corresponding output is provided. Following a shortdelay, a T₂ (reset) clock pulse is applied to the reset input of thecounter to return the counter to zero in preparation for anothercounting cycle. Consequently, the output of the counter may be read asthe whole blood flow rate.

The BCD data output of counter 337, which comprises a four digit BCDsignal, is applied to the A input of a first A/B select switch 338,which functions in a conventional manner to select one of two appliedBCD signals depending on an applied control signal. The strobe output ofthe counter is applied to the A input of a second A/B select switch 339.

The output of counter 336 is also applied through an AND gate 340 and adivide-by-60 counter 341 to the clock input of a display counter 342.AND gate 340 is enabled when the plasmapheresis apparatus is not in itsreinfuse mbde by a control signal developed on line 175 by controlcircuit 81 and applied to the remaining input of AND gate 340 through aninverter 344. When plasmapheresis apparatus 20 is operating in thereinfuse mode, the signal on control line 343 through inverter 344inhibits AND gate 340 to prevent the application of whole blood pumptach pulses to counter 342. The output pulses of counter 336, eachrepresenting the pumping of one milliliter of whole blood, areaccumulated by counter 342 on a real time basis, the latch input of thecounter being connected to ground. The counter continues to accumulatepulses until reset by application of a reset pulse on line 113.Consequently, the count in counter 342 represents the total volume ofwhole blood pumped over the time interval between reset pulses. The BCDdata output of counter 342 is applied to the B input of A/B selectswitch 338, and the strobe output of the counter is applied to the Binput of A/B select switch 339.

A/B select switches 338 and 339 are controlled by a control signaldeveloped by a display select switch 345. In the normal unactuatedposition of select switch 345 A/B select switches 338 and 339 select theA inputs. This causes the four digit data output signals of displaycounter 337 to be applied to a conventional display driver 346, whichconverts the signal to a seven digit signal for driving a trio ofdisplay panels 347-349. These display panels comprise the digitalreadout 62 on control panel 55. Necessary strobe signals are alsoprovided to the display panels by counter 337 through A/B select switch339 and respective display control transistors 352-355. A rate indicatorLED 350 is lit during WB rate display by the circuit display selectswitch 345 through inverting amplifier 351.

Upon actuation of the display select switch, A/B select switches 338 and339 select the B inputs and the four digit data output signal fromcounter 342 is applied through display driver 338 to display panels347-349 to provide a display of total volume processed. At the sametime, strobe signals from counter 342 are applied to the display panels347-349 through respective ones of transistors 352-354 and a decimalpoint is provided in display panel 348 by means of a transistor 355rendered conductive by closure of switch 345. A volume processed LEDindicator 356 is lit through a non-inverting amplifier 357 when switch345 is actuated. Thus, depending on the position of display selectswitch 345, readout 62 may indicate either the whole blood rate, inmilliliters per minute, or total whole blood volume processed, inliters.

Referring to FIG. 12, plasmapheresis apparatus 20 includes, inaccordance with the invention, a failsafe circuit for terminatingoperation of the apparatus in the event of a failure in the controlsystem. Referring to FIG. 12, within failsafe circuit 84 theanticoagulant pump stall signal on line 186 is applied through aninverter amplifier 360 to an isolation network 361, which provideselectrical isolation between the circuits of the stepper motor of theanticoagulant pump, and the failsafe circuitry. The input end of thenetwork is connected to the regulated unidirectional current sourceprovided for the other circuits of the system, and the output end isconnected to a separate power source 362 (+FS) within the failsafecircuit. This power source receives operating power from the motor powersupply 359, which supplies motors 70, 76 and 79.

The output of network 361 is applied to one input of an OR gate 363. TheWB pump motor overspeed/stall output, on line 128, is applied through anon-inverting amplifier 364 to a second input of OR gate 363. Similarly,the output of the replacement pump overspeed/stall circuit on line 135is applied through a non-inverting amplifier 365 to the remaining inputof OR gate 363. The output of OR gate 363, which is present upon theoccurrence of a stall condition in one or more of the three system pumpmotors, is applied to one input of an OR gate 366. The output ofemergency stop switch 98, available on a control line 367, is appliedthrough an inverter amplifier 368 to another input of OR gate 366. Theoutput of OR gate 366 is applied to the clock input of a JK-typeflip-flop 369. The Q output of flip-flop 369 is connected directly tothe failsafe motor stop line 85 to inhibit the operation of all motorsupon the occurrence of a clock pulse at the input of flip-flop 369. TheQ output of flip-flop 369 is also connected through an inverter 370 tothe emergency stop LED 105, and to an aural alarm 371 of conventionalstructure and operation. The Q output of flip-flop 369 is connectedthrough an inverter amplifier 372 to motor relay line 132 of thefailsafe system. The other motor relay line 133 is connected to thepositive polarity output of the motor power supply. As previouslydescribed, this power supply also supplies operating power to thevarious pump motors of the plasmapheresis apparatus, and to theregulated power supply 362 of the failsafe system.

In addition to monitoring the stall and overspeed detection circuits ofthe three system motors, failsafe circuit 84 also checks for actualmotion of the motors in the event of a bubble or fluid absence beingdetected. To this end, the output of the WB pump tach on line 119 is fedthrough an inverter amplifier 374 to an isolation network 375, whichprovides isolation in a conventional manner between the apparatus lowvoltage supply utilized by the WB motor control circuit and the powersupply 362 of the failsafe system. The output of isolation network 375is applied to a first JK-type flip-flop 376, which changes state inresponse to each applied tach pulse.

Replacement pump tach pulses on line 136 are applied through an inverteramplifier 377 and an isolation network 378 to the clock input of asecond JK-type flip-flop 379, which changes state in response to eachapplied tach pulse. Similarly, the anticoagulant pump tach pulses online 181 are applied through an inverter amplifier 380 and an isolationnetwork 381 to the clock input of a third JK-type flip-flop 382, whichchanges state in response to each applied tach pulse.

The outputs of flip-flops 376, 379 and 382 are applied to respectiveinputs of a three input OR gate 383, causing the output of the gate tochange state periodically as tach pulses are applied to any one of thethree flip-flops. The output of OR gate 383 is applied through aninverter amplifier 384 to the parallel/serial (P/S) control input of ashift register 385. This register, which comprises a is normally in aparallel mode, is conditioned to a serial mode upon the application ofan input signal on its parallel/serial enable input. Once enabled in itsserial mode, shift register 385 provides an output following theapplication of four clock pulses to its clock input.

In normal operation shift register 385 is inhibited from operating inits serial mode by a reset signal applied to its reset input by bubbledetector No. 2 (BD2) through a non-inverting amplifier 386 and a NANDgate 387. NAND gate 387 is enabled by a control signal present oncontrol line 273 whenever the run or reinfuse modes are selected, asprovided by control circuit 81. The signal on line 273 is fed through anisolation network 388 to the remaining input of NAND gate 387. Theoutput of BD2, being logic low except upon the occurrence of a fluidabsence, normally prevents the output of gate 387 from assuming otherthan a logic high. However, if the output of BD2 becomes logic high, andif the bubble detector enable line 273 is also logic high, NAND gate 387produces a logic low which removes the reset signal from shift register385.

If any one of the system tachometers is providing output pulses at thetime the reset pulse is removed by the occurrence of a bubble, shiftregister 385 is conditioned to a serial mode and begins to count. Afterthe application of four clock pulses to the clock input of the register,an output is produced by the register which is applied to the remaininginput of OR gate 366. This conditions flip-flop 269 to its alarm state,and operation of the apparatus is interrupted.

To insure that flip-flop 269 will always be in a reset state in theabsence of a fault condition, a power-up circuit 389 is provided tosupply an initial reset pulse to the reset input of flip-flop 369 uponpower-up of the apparatus. The necessary clock pulses for shift register385 are supplied at a one second rate by a conventional clock circuit390. This clock circuit may include conventional oscillator andfrequency divider circuits (not shown) for deriving the desired onesecond clock signal. The output of clock 390 is also applied through apair of serially-connected inverters 391 and 392 to the reset inputs offlip-flops 376, 379 and 382 to reset these devices following each clockperiod.

Thus, following occurrence of a bubble or fluid absence at the secondbubble detector, if any one of the pumps continues to run for more thanfour seconds a stop sequence is initiated which removes all operatingpower from the pumps. Once this condition has occurred, it can only bereset and operation resumed by removing all power from theplasmapheresis apparatus so that powerup circuit 390 resets flip-flop385.

While the invention has been shown in conjunction with plasmapheresisapparatus, it will be appreciated that the invention can also beutilized in other blood fractionation procedures where components otherthan plasma are separated and collected.

While a particular embodiment of the invention has been shown anddescribed, it will be obvious to those skilled in the art that changesand modifications may be made therein without departing from theinvention in its broader aspects, and, therefore, the aim in theappended claims is to cover all such changes and modifications as fallwithin the true spirit and scope of the invention.

We claim:
 1. In a blood fractionation apparatus operable in conjunctionwith a disposable fluid flow system for separating and collecting ablood fraction from whole blood, and including at least one motor-drivenpump for conveying blood through the flow system, a tachometerassociated with the motor, and a monitoring device providing an alarmsignal in the presence of a fluid absence in the system, a failsafecontrol circuit comprising, in combination:a flip-flop responsive toapplied tachometer pulses from the pump motor for producing an alarmcontrol signal; a series-parallel counter having a reset input, a clockinput and a series/parallel enable input, said counter requiring apredetermined number of applied clock pulses following application of aserial enabling signal for producing an output; means for applying saidflip-flop output signal to said parallel-serial enable input to enablesaid counter to a serial mode upon occurrence of said tach pulses; meansfor applying said fluid absence alarm signal to said reset input toenable operation of said counter upon the occurrence of a fluid absencein the system; means for applying clock pulses to said counter wherebysaid counter counts to zero over a predetermined time interval uponbeing conditioned to a serial mode at said serial-enable input and uponbeing enabled at said reset input; and means responsive to the output ofsaid counter for terminating operation of the pump.
 2. A bloodfractionation apparatus as defined in claim 1 wherein saidseries-parallel counter is a programmable counter, and a predeterminedcount is parallel-loaded into said counter.
 3. A blood fractionationapparatus as defined in claim 2 wherein said programmable counter isclocked at a one second rate, and said delay period is equal to saidparallel-loaded count.
 4. A blood fractionation apparatus as defined inclaim 3 wherein said parallel-loaded count is four and said delay periodis four seconds.
 5. In a blood fractionation apparatus operable inconjunction with a disposable fluid flow system for separating andcollecting a blood fraction from whole blood, and including at least onemotor-driven pump for conveying blood through the flow system, atachometer associated with the motor, and a monitoring device providingan alarm signal in the presence of a fluid absence in the system, afailsafe control circuit comprising, in combination:a flip-flopresponsive to applied tachometer pulses from the pump motor forproducing an alarm control signal; a series-parallel programmablecounter having a reset input, a clock input, a parallel data input and aserial/parallel enable input, said counter producing an output uponcounting down from a parallel-loaded count to zero in the absence of areset signal and following application of a serial enabling signal;means for applying a predetermined initial count signal to said paralleldata input; means for applying said flip-flop output signal to saidparallel-serial enable input to enable said counter to a serial modeupon occurrence of said tach pulses; means for applying said fluidabsence alarm signal to said reset input to enable operation of saidcounter upon the occurrence of a fluid absence in the system; means forapplying clock pulses to said counter whereby said counter counts tozero over a predetermined time interval upon being conditioned to aserial mode at said serial-enable input and upon being enabled at saidreset input; and means responsive to the output of said counter forterminating operation of the pump.
 6. A blood fractionation apparatus asdefined in claim 5 wherein said programmable counter is clocked as a onesecond rate, and said delay period is equal to said parallel-loadedcount.
 7. A blood fractionation apparatus as defined in claim 6 whereinsaid parallel-loaded count is four and said delay period is fourseconds.
 8. In a blood fractionation apparatus operable in conjunctionwith a disposable fluid flow system for separating and collecting ablood fraction from whole blood, and including at least one motor-drivenpump for conveying blood through the flow system, a tachometerassociated with the motor, and a monitoring device providing an alarmsignal in the presence of a fluid absence in the system, a failsafecontrol circuit comprising, in combination:a series-parallel counterhaving a reset input, a clock input and a series/parallel enable input,said counter requiring a predetermined number of applied clock pulsesfollowing application of a serial enabling signal for producing anoutput; means responsive to said tachometer pulses for enabling saidcounter to a serial mode; means for applying said fluid absence alarmsignal to said reset input to enable operation of said counter upon theoccurrence of a fluid absence in the system; means for applying clockpulses to said counter whereby said counter counts to zero over apredetermined time interval upon being conditioned to a serial mode atsaid serial-enable input and upon being enabled at said reset input; andmeans responsive to the output of said counter for terminating operationof the pump.
 9. A blood fractionation apparatus as defined in claim 8wherein said means for terminating operation of the pump include aflip-flop responsive to the output of said counter.